1. Field of the Invention
The present invention relates to a system for incinerating organic waste water and volatile organic compounds and a method therefor and more particularly, an evaporative and regenerative waste water incineration system for economically and efficiently removing the organic compounds by oxidizing the waste gas generated from evaporated waste water including the organic compounds using a regenerative thermal oxidizer.
2. Description of the Related Art
Generally, volatile organic compounds including a total of hydrocarbon compounds are materials generally created in chemical factories, waste water treatment plants and during the printing works in car manufacturing factories, and cause the photochemical smog, warming of the Earth, destruction of ozone layer in the stratosphere, and so on, and very fatally toxic to human body such as developing cancer, etc. and the human environment.
The known techniques to treat the volatile organic compounds are incineration, absorption for removal, adsorption, cooling condensation, biological treatment and layer separation methods, etc. And especially regenerative thermal oxidation method is widely used.
A Regenerative thermal Oxidizer (now referred to as RTO) is operated by incinerating the waste gas including the volatile organic compounds, and collecting the heat generated during the incineration through a ceramic filler material thereby greatly reducing the operation expenses of the system, and minimizing an installation space. The treatment efficiency of the RTO is very high over 99%, and a second contamination is little, and if the concentration of the volatile organic compounds in the waste gas is over 300 vppm, a supplementary supply of energy is not necessary by using the incineration energy from the system, itself.
Describing its operation more detail, the RTO maximmably collects the waste heat energy discharged from the waste gas and turns the energy to preheat introduced gas. For this purpose, it employs ceramic which is directly heated and cooled for its regeneration instead of a typical heat exchanger.
That is, when using a shell and tube type heat exchanger or a plate type heat exchanger for the heat exchange of gas, the temperature difference of the gas between the inlet and the outlet of the heat exchanger is 100 to 200xc2x0 C. thereby limiting the usage. However, the ceramic has its maximum service temperature by 950xc2x0 C., and when regenerating, the temperature difference between the inlet and the outlet can be reduced to 20xc2x0 C. thereby achieving 98% of the heat recovery rate.
FIGS. 1 and 2 show the operation states of forward/rearward direction in the typical RTO. After heating a furnace placed between ceramic layers 1, 2 disposed on the left and right sides of the RTO to be appropriate for the operation of the furnace at the start of the operation, the waste gas is introduced.
The waste gas is preheated up to the temperature of the furnace passing the ceramic layer 1, and the organic gas in the waste gas starts its oxidation and while passing through the furnace for a certain time period, all the organic compounds are oxidized at a temperature of about 800xc2x0 C.
At this time, while the treated gas at a high temperature passes though the ceramic layer 2, the gas discharges out almost all heat so that the gas is cooled just down to a temperature of 10 to 30xc2x0 C. higher than the temperature of the inlet in the ceramic layer 1.
At this time, after a while, the inlet path for the gas is switched as shown in FIG. 2.
The switching operation shown in FIGS. 1 and 2 is repeated with a certain interval of time (about 1.5 to 3 minutes) thereby minimizing the energy for the gas incineration.
The system shown in FIGS. 1 and 2 is called a 2-bed type RTO, and the 2-bed type RTO is an economical system. However, not-treated gas existing on the ceramics of the RTO during the switching of the valves and other not-treated gas passing through the furnace of the RTO in a roundabout way are discharged at a time during the switching of the valves so that the removal efficiency of the whole organic compounds is around 95% due to the discharge of the not-treated gas.
To address this problem, a 3-bed type RTO or a gas buffer can be used. The case of using the buffer is shown in FIG. 3.
That is, the incineration system comprises an RTO, a gas buffer and a blower.
The operation of forward direction by using the buffer 12 is described as follows:
The not-treated waste gas from the processes is introduced into a ceramic layer 3 on one side of the 2-bed type RTO with a valve 5 open. The introduced gas at room temperature is heated up to 800xc2x0 C. for oxidation by the regenerative ceramic so that the organic volatile compounds (VOC) in the air is oxidized. The temperature of the gas after oxidation is about 830xc2x0 C. which is 30xc2x0 C. higher than that of the regeneration ceramic. The gas at this temperature is cooled down passing through a ceramic layer 4 at the other side. Most of the heat is transmitted to the ceramic layer 4 thereby increasing the temperature of the ceramic 4. The cooled-down gas passes through a valve 8, the blower 13, and a valve 10 in turn and is discharged to the atmosphere.
As described above, during the operation of the forward direction, the valve 5, 8 are open and the valves 6, 7 are closed. A buffer valve 9 at the front of the gas buffer is closed.
While the operation of the forward direction is maintained for about 2 minutes, the ceramic of the ceramic layer 3 preheats the gas and is cooled down. The ceramic layer 4 absorbs the heat of the heated gas and is heated. At this time, the introduction of the gas is started with the operation start of the rearward direction.
The operation conditions in the forward direction and the rearward direction are the same, and the introduction direction of the waste gas is changed to the ceramic layer 4 on the other side. There exists a switching time between the operation of the forward/rearward direction.
Since the valves 5,8 of the rearward direction are closed and the valves 6,7 are open, not-treated waste gas present between the ceramic layer 3 and the valve 5 passes through the valve 7 by the blower 13, and is discharged through the valve 10 to the atmosphere.
To prevent this, by using the gas buffer 12, the buffer valve 9 is open, and the valve 10 of a pipe leading to a smokestack is closed.
Therefore, the not-treated gas is collected into the gas buffer 12 through the buffer valve 9, and the treated gas on the upper side of the gas buffer 12 is directly discharged out of the smokestack.
After the switching time, the gas path at the back side of the RTO is turned to the discharge pipe, and the buffer valve 9 is closed.
There is provided a diaphragm inside the gas buffer 12 to minimize the mixing of the introduced gas. The lower side of the buffer is connected to the inlet line for not-treated gas, and the upper side of the buffer is in flow communication with the discharge pipe to the atmosphere. The not-treated gas stored in the buffer is automatically circulated to the front of the RTO with the valve 11 open, and the inside of the buffer is changed with a gas introduced from the atmosphere until the next switching time.
Meanwhile, in chemical factories, the waste water treatment and cars manufacturing companies, large amount of other kinds of waste water beside the above organic compounds is generated. When the concentration of the organic compounds in the organic waste wate is low (e.g., COD lower than 5,000 ppm), it is treated with active oil treatment, but in case of high concentration (e.g., COD higher than 10,000 ppm), the active oil treatment is not sufficient and not economical so that it is treated by incinerating.
At this time, the waste water incineration using a typical incineration furnace is operated by introducing the waste water including organic compounds (VOC included) into the incineration furnace, and oxidizing the organic compounds in the waste water by heating the waste water up to 950xc2x0 C. However, even though the heat exchanger can be used to collect the energy, the recovery rate of the heat is very low and the operation expenses of the incineration furnace is large.
Therefore, the installation of such a typical incineration furnace results in an increased production expenses due to its highly increased expenses for the antipollution measures thereby requiring the development of an economical treatment system for waste water at low-energy consumption.
Typically, in the incineration system, the organic waste water is directly sprayed into a high temperature of the furnace so as to evaporate the waste water in the furnace, and oxidize the gaseous organic compounds. In case that the waste water includes salt, a quenching type incineration furnace as shown in FIG. 4 is employed, and in case of the waste water without salt, the heat exchangeable incineration furnace as shown in FIG. 5 is employed.
However, in the typical incineration method as described above, the waste water is all directly sprayed into the furnace so that heat energy is oversupplied thereinto, and because of the use of just recovery heat exchanger, the heat recovery rate is very low with absence of medium for heat exchange.
The present invention provides an incineration system for treating organic waste water and volatile organic compounds while providing the same efficiency with that of the incineration systems of related arts or better and saving the operation expenses for the system by at least 80%.
The main ideas and objects of the present invention can be summarized as follows in three points.
First, a regenerative thermal oxidizer (now herein after referred to as RTO) for use in treating waste gas including organic compounds is employed for treating waste water and an evaporator is employed for generating waste gas for the above purpose.
Second, heat energy created from the oxidation of the organic compounds in the waste gas can be fed back to be used as a source to operate the evaporator while maximizing the characteristics of the RTO consuming a little energy for the oxidation.
Third, the remnant not-treated gas present from the former stage generated during the switching of the operation of forward/rearward direction is accumulated at a certain space before being treated with batch-processing at a later stage.
According to one aspect of the present invention, there is provided an incineration method for incinerating waste gas in the RTO after evaporating the organic waste water including organic compounds by heating up to a certain temperature using an evaporator.
According to another aspect of the present invention, there is provided an evaporative and regenerative incineration system for organic waste water in which waste gas is generated by evaporating organic waste water including organic compounds, the generated waste gas is oxidized with air, and the heat energy from the oxidization is regenerated to evaporate the waste water.
It is to be understood that both the foregoing general description and following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.